The present invention relates to a method for manufacturing a contact arrangement for a vacuum switching tube having a contact carrier and a contact piece that is joined to the contact carrier in a vacuum using a soldering material.
A method for manufacturing a contact arrangement for a vacuum chamber is described in German Patent Document No. 196 32 573 A1, in which the contact carrier in a vacuum is coated with a contact layer through sintering an appropriate powder and its subsequent solidifying. It is further known to solder a contact carrier to a contact piece in a vacuum using a soldering material that is arranged in between, by melting the soldering material and pressing contact carrier and contact piece together. Mechanical, frictional-locking bonds between contact piece and contact carrier are also known, reference being made, by way of example, to German Patent Document No. 44 47 391 C1 and German Patent Document No. 195 34 398 A1.
In FIGS. 1a and 1b, there is a schematic illustration of a known method for producing a soldered connection between a contact carrier 1 and a contact piece 10 using an intermediate layer of a soldering material 11, for example a soldering disk. In this context, contact piece 10 is preferably provided with a saucer-shaped recess 101, into which are set soldering disk 11 and then contact carrier 1 at its mounting end. After being heated in the vacuum, soldering disk 11 melts and produces soldered connection 30 between contact carrier 1 and contact piece 10. In this method, it is disadvantageous that in the hanging arrangement of contact piece 10 on contact carrier 1, a sufficient positive locking between contact piece and contact carrier must be present during the production of the soldered connection in order to prevent contact piece 10 from falling away in the melting of the soldering disk. In the hanging arrangement, in the case of larger contact pieces, it is frequently necessary, during the soldering process in the vacuum, to employ auxiliary structures in order to prevent the contact piece from falling away or, on the other hand, to provide for a supplementary positive locking of contact piece 10 on contact carrier 1.
An objective of the present invention is to provide a method by which a contact arrangement having soldered bonding sites can be manufactured reliably and more simply using a smallest possible optimal quantity of soldering material.
The present invention provides a method by which the contact piece is directly pressed flat onto the contact carrier, leaving a gap along the contact surface, and the soldering material is arranged in areas directly bordering on the gap of the contact surface between the contact piece and the contact carrier, and subsequently, in a vacuum, through applying heat, the soldering material is brought to the melting point and the melted soldering material penetrates into the gap of the contact surfaces between the contact carrier and the contact piece.
The method according to the present invention can be applied with particular advantage to the manufacture of contact arrangements for vacuum switching tubes. The method according to the present invention makes it possible for the contact surface between contact carrier and contact piece to be wetted with soldering material on virtually its entire surface, i.e., sufficiently. In addition, the bond between contact carrier and contact piece is strengthened through the melted soldering material rising in the gapxe2x80x94the annular gapxe2x80x94between contact carrier and contact piece, the gap being mainly vertical and, towards the exterior, adjoining the contact surface between contact carrier and contact piece. Depending on the type of configuration, an optimal dosing is possible of the quantity of soldering material that is required to achieve the sufficient soldered connection between contact carrier and contact piece. In particular, the method according to the present invention makes it possible, in a simple manner, to produce a contact carrier having a contact piece hanging from it, i.e., in the hanging position. Applying the method according to the present invention to the production of vacuum switching tubes makes it possible to manufacture, for example, all of the soldering points of a preassembled vacuum switching tube in one processing step, i.e., in one oven cycle.
According to one version of the present invention, a contact piece is used that has a planar, saucer-shaped recess, into which the contact carrier at its mounting end is set, an annular gap between contact piece and contact carrier being formed at the planar gap of the contact surface, and the soldering material being placed in ring-like fashion around the contact carrier at the annular gap emerging between contact carrier and contact piece, so that after the melting, the soldering material is pulled by gravity and capillary action into the annular gap and the gap along the saucer-shaped recess. In this variant of the method according to the present invention, a virtually full-surface wetting of the contact surface between the contact carrier and the contact piece is achieved by the molten soldering material flowing and pressing into the gap from the sides. In addition, however, as a result of the solder collecting in the lateral vertical gaps, a good bond of great stability is achieved between contact carrier and contact piece.
According to a further version of the present invention, however, it is also possible to introduce the soldering material via bore holes that lead through the contact carrier to the contact surface between the contact carrier and contact piece. According to one version of the present invention, a contact piece is used that has a planar, saucer-shaped recess, into which the contact carrier at its mounting end is set, and, additionally, a contact carrier is used, which has at least one bore hole running through the contact carrier to the contact surface having the saucer-shaped recess, and the soldering material is poured into the bore holes of the contact carrier so that, after the melting, due to gravity and capillary action, the soldering material presses into the gap along the saucer-shaped recess, including into the circumferential annular gap.
For these process techniques, the solder can be placed into the bore holes of the contact carrier in the form, for example, of wire. In addition, these bore holes make possible an improved degasification of the space between the contact piece and contact carrier.
In a further embodiment of the method, it is proposed that a contact piece may be used that has a planar, saucer-shaped recess, into which the contact carrier at its mounting end is set, and a contact carrier be used, which, at its contact surface adjoining the saucer-shaped recess, has at least one recess, and the soldering material be poured into the recess of the contact carrier, so that, after the melting, the soldering material penetrates, due to gravity and capillary action, into the gap along the saucer-shaped recess, including into the peripheral annular gap.
In all of these cases, during the soldering, an oversupply of soldering material rises up again through the vertical gaps and bore holes, so that an optimal wetting and dosing of the soldering material is possible.
A further example of a method according to the present invention provides setting a contact piece into a saucer-shaped recess of a contact carrier and applying the soldering material in the form of a soldering paste onto the contact piece and over the annular gap end between the contact carrier and contact piece, so that, after the melting, the soldering material is pulled by gravity and capillary action into the gap along the saucer-shaped recess.
Here, too, it is possible to fix the contact piece on the contact carrier without a positive-locking or frictional connection. This variant is designed especially for securing contacts in the non-hanging position. As a solder paste, it is preferred to use one having a silver or copper base, the binding agent or binders evaporating during the heating-up process in a vacuum, leaving no residue. During the time when the soldering material is in a molten liquid state in a vacuum, the contact piece is held by the surface tension of the soldering material and/or the latter""s adhesive force, so that precise positioning is also assured.
To achieve a good contact soldering and sufficient stability of the bond between contact piece and contact carrier, it is proposed that an amount of soldering material be used such that, after the complete wetting of the gap between contact carrier and contact piece, the remaining molten mass of solder is used to seal the solder supply points, for example, as a residual plug seals the solder supply points.
Thus the method according to the present invention makes it possible to satisfactorily manufacture soldered connections between contact pieces and contact carriers even in a hanging arrangement, the method being particularly advantageous when applied in connection with vacuum switching tubes. The method according to the, present invention can be refined and applied in that the contact arrangement composed of contact carrier, contact piece, and soldering material is preassembled into a unit having further components constituting the vacuum switching tube, components that are bonded to each other at soldering points using soldering material, along with a second contact arrangement, a shielding part, cover parts, insulating parts, and a bellows, and the preassembled unit being placed into a vacuum soldering oven, one of the two contact arrangements being in the hanging position of the contact piece and, under the influence of the vacuum, the simultaneous melting of all of the soldering material being effected at all of the soldering locations by heat, so that all of the soldered connections of the vacuum switching tube are produced in one process step.
According to the present invention, therefore, the soldering points of a piece to be connected, i.e., specifically, of the contact piece having a contact carrier, can be produced both in the hanging position as well as in the standing position. Since the soldering material penetrates into the gap between contact piece and contact carrier only after melting, there is no falling away due to excessive solder melting, which is the case when the soldering material is arranged beforehand between contact carrier and contact piece. For carrying out the method according to the present invention, at least for the soldered connection to be generated in the hanging position, a mechanical, clamping bond or mechanical positive-locking fit is sufficient to avoid a falling away of the contact piece from the contact carrier during the production of the soldered connection.
In order to prevent a not-yet-soldered contact piece from falling away from the contact carrier during a soldering process in the hanging position, the proposal is made to provide for a mechanical and/or friction-locking and/or form-locking bond at least in areas between the contact piece in the contact carrier by configuring them appropriately outside of the contact surfaces of contact piece and contact carrier forming the planar gap, the bond being produced in the assembly of contact piece and contact carrier. A mechanical bond of this type between contact piece and contact carrier can be provided, for example, through creating a profiling at least in areas on the lateral surface of the contact carrier and/or, if appropriate, also on the interior-side lateral surface of the recess of the contact piece, to achieve a light clamping of the contact carrier in a saucer-shaped recess of the contact piece for sufficient stability in the hanging position. This profiling, for example, can be provided as milled knobs or knurls having fins and depressions, or also, for example, by only a single profiling in the shape of a protruding rise on the lateral surface of the contact carrier.
In the assembly of the contact carrier and contact piece, instead of achieving a mechanically stable bond for a hanging position using a skeleton form, a flanging, or profiling, the contact pieces and contact carriers to be bonded to each other can also be joined using a friction- and positive-locking bond, such as in a bayonet lock. The minimal annular gap remaining in this context can be supplied, for example, from a soldering material supplyxe2x80x94depositxe2x80x94on the contact carrier using sufficient solder, for example using a corresponding piece of soldering wire.
The projections or grooves of a bayonet lock of this type can be shaped so as to taper into a slight cone, so that by twisting the contact piece in a contact carrier made of soft copper, a clamping screw connection is achieved having a good supporting capacity. In this context, it is possible to achieve a good, planar, and friction-locking bond between the contact piece and the contact carrier. At the same time, the groove of the bayonet lock bond can function as the solder supply channel and then as the soldered connection point for the two parts to be bonded subsequently, using solder.
The contact carriers and the contact pieces, in accordance with the application purpose and the load of the vacuum switching tube, can be made from known materials, such as were described in the documents mentioned above regarding the related art.